AsO, add a drop of HCl, and pass HS through the solution, and observe the yellow precipitate of As S

(c) Attach another tube containing an arsenic mirror to an apparatus evolving dry H2S, and warm the mirror gently it will be converted into yellow As¿S3. Now pass dry HCl through the tube (without warming), and observe that the sulphide remains unaltered. (Compare corresponding Sb reactions, 74, 6, c).

(d) Allow a current of AsH, to pass through a solution of silver nitrate : a black precipitate of Ag will be produced, and As2O, will be found in solution along with HNO3 liberated from the AgNO3. Filter from the Ag, and very cautiously neutralize the free acid with highly diluted (NH4)HO, when a yellow precipitate of AgAsO will be formed. (Compare corresponding Sb reaction, 74, 7.)

3

6. Compounds of arsenic, when treated with Zn and strong solution of KHO, are converted into AsH, by the action of the nascent hydrogen. If this reaction be performed in a test tube, and the gas escaping be held near a piece of paper moistened with AgNO3, a bluish black coloration is produced by the formation of AsAgg. (Sb compounds give no similar reaction.)

7 (Reinsch's Test).—Add to the solution of arsenic, HCl and a few strips of bright copper wire or foil: As is deposited on the copper, which may be removed from the solution, dried by filter paper, and heated in a dry test-tube to obtain the octahedral crystals of As2O3

8. Dry reactions.

Place the dry arsenic compound at a (Fig. 17), in a drawn-out hard glass tube. Then place above it at b a small rod of well-ignited charcoal, and heat the portion containing the charcoal until it is red hot. This will

a

FIG. 17.

cause the glass to soften, and the tube will bend so as to bring the portion a into the flame. The arsenic compound will volatilize and be decomposed by the red-hot charcoal, and a metallic mirror will form at c.*

9. Place the dry arsenic compound in a bulb tube as at a (Fig. 18), along with a mixture of equal parts of dry Na,CO, and KCN, and heat the bulb. A mirror

FIG. 18.

of As will form at b, which may be further tested by the reactions mentioned for the mirror obtained in Marsh's test (75, 5, 6). If any moisture be deposited on first heating the tube, remove it by inserting a small coil of filter paper.

10. The above reaction is more delicate when the mixture is heated in a current of dry CO2. For this

* Non-volatile compounds of As must be mixed with dry charcoal powder, and heated in a similar tube, having in addition a small bulb at the lower end to contain the mixture.

purpose, the arsenic compound is pounded in a mortar with a perfectly dry mixture of three parts Na2CO3 with one part of KCN, and placed at a in the tube ab (Fig. 19), through which a slow current of dry CO2 is

FIG. 19.

led, and the whole tube gently heated until every trace of moisture is expelled. When this is the case the tube is more strongly heated at a, and the mirror is obtained at b; traces of arsenic escape condensation, and therefore a slight garlic odour is observed at the extremity of the tube. Antimony compounds treated in this way yield no metallic mirror.

11. Arsenic compounds, when mixed with Na2CO, and heated on charcoal by the blow-pipe flame, are reduced to metallic arsenic, which at once volatilizes, and may be recognized by the characteristic odour resembling garlic.

TABLE E.

GROUP II.

76. Separation of Arsenic, Antimony, and Tin (Sub-Group B).

Solution in (NH4)2S, contains sulphides of As, Sb, and Sn. Add HC1 until acid the metals are re-precipitated as sulphides. Filter, wash precipitate with hot ware: till 'ree from HCI; digest precipitate with one or two pieces of solid (NH4)2CO3 and H2O. Filter.

Reactions of the Metals of the Iron Group.

77. Metals whose sulphides and hydrated oxides are insoluble in water, and are precipitated on addition of the group reagent (NH4)2S in presence of (NH)HO and NH4Cl.

Iron, Nickel, Cobalt, Zinc, Aluminium, Manganese, and Chromium.

IRON. Fe, c.w. 56. Ferrous Salts.

1. (NH4)2S produces a black precipitate of FeS, insoluble in alkalies, but soluble in HCl. In dilute solutions of ferrous salts (NH4)2S produces at first a green colour; on standing, however, FeS separates as a black precipitate.

2. KHO or (NH)HO produces a white precipitate of ferrous hydrate Fe(HO)2, which rapidly acquires a dirty green, and ultimately a reddish brown colour, owing to absorption of oxygen and conversion into ferric hydrate Fe,(HO).

3. Carbonates of the alkalies precipitate FeCO3

G

(white), which rapidly darkens in colour owing to absorption of oxygen.

4. K4Fe(CN)。 produces a white precipitate of K2Fe2(CN)6, which rapidly becomes blue by oxidation to Fe(CN)12 (Prussian blue). It is insoluble in acids, but is decomposed by alkalies.

5. K Fe(CN)6 produces a blue precipitate of Fe Fe2(CN) 12 (Turnbull's blue), also insoluble in acids, but decomposed by alkalies.

6. KCNS produces no coloration.

7. Ba CO produces no precipitate in cold solutions of ferrous salts,

8. Fused with borax in the oxidizing flame, yellowish red beads are produced; in the reducing flame the beads become green. (See also 59.)

=

Ferric Salts.-1. H2S in acid solutions produces a precipitate of sulphur, and the salt is reduced to protosalt, thus FeCl + H2S 2 FeCl2 + 2 HCl + S. 2. (NH4)2S produces a black precipitate of FeS mixed with sulphur, insoluble in excess of the reagent and in alkalies, but soluble in HCl and in HNO3. In dilute solutions of iron only a greenish coloration is produced.

3. KHO or (NH4)HO produces a brownish red precipitate of Fe2(HO)6, insoluble in excess of either reagent.

4. K4Fe(CN)6 produces a precipitate of Fe(CN)12 (Prussian blue), insoluble in HCl, soluble in C2H2O4, and decomposed by KHO or NaHO with separation of Fe (HO).

5. K3Fe(CN)6 changes the colour of the solution to reddish brown, but does not produce a precipitate.